The invention relates to a slip ring of the type wherein electric connection between a fixed member and a movable member is established by physical contact between a conductive plate and a contact element.
A slip ring of the type mentioned is used as an electric connecting device for transmitting an electric signal between a movable member and fixed member and is incorporated, for example, in a steering device of an automobile wherein it couples a horn signal or the like from the steering wheel (movable member) side to the bearing (fixed member) side.
Conventional slip rings typically have such a structure that, for example, a plurality of ring-shaped conductive plates corresponding to a required number of circuits are located in a concentrical relationship on a surface of a fixed member while a number of contact elements corresponding to the individual conductive plates are located in a predetermined spaced relationship in a diametrical direction on a movable member, whereby electric connection between the movable member and the fixed member is established by sliding contact of the contact elements with the conductive plates when the movable member is rotated.
Such a conventional slip ring is sometimes used in a severe condition in which the temperature varies very widely. If the slip ring is exposed, for example, from a low temperature condition to a high temperature condition, then air thus warmed will be cooled suddenly near around boundary faces of the conductive plates so that water in the air will be condensed into dew. Accordingly, it is a problem that, if the slip ring is exposed to a low temperature condition again, drops of water of the dew may freeze into ice on the slip ring. Once such frozen pieces of ice resulting from dew condensation appear on surfaces of the conductive plates, they will interrupt electric connection between the conductive plates and the contact elements, which will result in failure in electric connection of the slip ring which is a serious defect to the slip ring.
An improved slip ring has been already provided wherein a heat source such as a heater is located near conductive plates in order to prevent such condensed water from freezing. The slip ring, however, has a drawback that the overall size thereof is increased and its production cost is increased remarkably.